Abstract.We study the impact of 1/f noise on the Planck Low Frequency Instrument (LFI) observations (Mandolesi et al. 1998) and describe a simple method for removing striping effects from the maps for a number of different scanning strategies. A configuration with an angle between telescope optical axis and spin-axis just less than 90• (namely 85 • ) shows good destriping efficiency for all receivers in the focal plane, with residual noise degradation < 1 − 2%. In this configuration, the full sky coverage can be achieved for each channel separately with a 5• spin-axis precession to maintain a constant solar aspect angle.

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Abstract. Future space mission like MAP and Planck will be able to shade new light on our knowledge of the Universe thanks to their unprecedented angular resolution and sensitivity. The far sub-degree angular resolution is obtained coupling usual detectors, radiometers and/or bolometers, to an optical system, namely a telescope. The wealth of cosmological information is encoded at high values (∼ 1000) which can be reached with resolution of about 10 . Distortions of the main beam resulting from the current focal plane arrangement and the optical design of the Planck satellite will degrade angular resolution and sensitivity per resolution element possibly compromising the final results. The detailed design of the Planck telescope is continuously changing with the aim of optimizing its performance. In the present work we present a methodological study on the relation between telescope optical design, focal plane arrangement and optical performances, focussing on the dependence of angular resolution on primary mirror aperture. Different independent approaches have been developed to quantify the impact of main beam distortions on cosmic microwave background (CMB) science yielding nearly the same results. The socalled PHASE-A telescope is unacceptable with respect mission main goals. Larger telescopes (namely with effective aperture > ∼ 1.5 m) are therefore preferable. This paper is based on the Planck LFI activities.

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Abstract. In the context of the COBRAS/SAMBA mission study 1 , we discuss in-flight calibration of extended sky maps of the microwave sky using celestial sources. We simulate the observations in order to assess the accuracy obtainable for absolute and relative calibration of the Low Frequency Instrument (LFI), operating in the 30 − 130 GHz range. Accurate calibration can be achieved using the CMB dipole signal, ∆T D . With conservative assumptions on the effect of Galactic contamination, we find that the CMB dipole will provide absolute calibration accuracy ∼ 0.7% (limited by the COBE-DMR uncertainty on ∆T D ) on time-scales of about 10 days at all frequencies and for the entire mission lifetime. Long-term calibration with accuracy < 0.2% can be obtained using the spacecraft orbital velocity. Additional, independent calibration will be provided by the observation of external planets. We also describe the capability of the proposed scanning technique to detect and remove long-term instrumental drifts, and show that these effects, if present, can be controlled and removed with an overall negligible impact on the data uncertainty.